OK, I'm not saying that these "realistic" games should necessarily go into infinite detail. I think a certain amount of license is given, and accepted, with regards to entering/exiting a vehicle but jumping into a closed-cockpit plane whilst it is in the air is stretching things a bit far, don't you think?
Fine, have easy access while it's on the ground but not while it's flying - come off it, it's just silly at best and ridiculously unrealistic at worst.
I'm not knocking the game as a whole (not having played it, tbh, although I have others in the BF series) but it's sold on it's realism and this is in no way anywhere near realistic. If you jump out of a plane, you should not be able get back into it (or another one) - unless it's a crazy "skydive" game which involves dropping from one plane to another.
Like this guy does (skip to 1:30 for start of jump):